The present invention relates to a process for making a non-polar polymer material dyeable with an acid dye.
From Canadian Pat. No. 972,429 which relates to a plasma generator using microwave energy, it is known that desirable characteristics can be imparted to various materials such as plastics, via a plasma treatament. For example, "cross-linking" a desirable characteristic for certain plastic materials can be achieved on the surface of such a material when exposed to a gaseous plasma. Crosslinking a plastic film, such as a polyethylene film, can greatly improve bonding and printing characteristics of the film. It is also possible to graft various molecules to free radical sites created by plasma treatment on polymeric fibers. Through crosslinking, the dyeability and washability characteristics of certain textiles, e.g. polyester and other synthetic materials, can be greatly improved. Exposure to a plasma also has been found to substantially reduce shrinkage to natural fibers, such as wool. Certain organic vapors in a plasma can be made to form solid polymer films on a substrate passed through the plasma. By this method, a layer of very thin polymer can be made which is free of defects, which is useful for various industrial purposes, such as, encapsulation of electronic components or protection of surfaces against corrosion.
Using plasma, the bonding characteristics of films or fibers prepared from natural or synthetic polymeric materials or combinations thereof can be improved. It is possible to form protective oxide or nitride layers on the surfaces of metals or semiconductors, to synthesize useful organic or inorganic molecules, and to obtain laser action by an especially developed process. Details of these processes, familiar to those skilled in the art, are not given here. The "Large Volume Microwave Plasma Generator" (LMP) described in Canadian Pat. No. 972,429 is capable of efficiently producing atoms and other chemically active species which can be highly advantageous in the above processes.
It is an object of the present invention to modify the surface of a non-polar polymeric material by low temperature microwave plasma in order to render that material dyeable with conventional acid dyes.
In constrast to other fiber materials such as wool, silk, nylon, cellulose and polyester, non-polar polymeric materials, such as polypropylene, are not receptive to acid dyes. Traditionally, polypropylene in fiber manufacture has been colored by mass pigmentation. This coloring technique provides good color wear resistance but has the disadvantage of expensive pigment costs and high inventory costs. Also, the use of massive amounts of pigments on the non-polar polymeric fibers harms certain intrinsic fiber properties, such as uniformity in the fibers which outweighs the color wear resistance advantage. For these reasons, development efforts have been directed towards making non-polar materials such as polypropylene, receptive to acid dyes.
It has now been found that non-polar polymeric material can be made receptive to acid dyes by treating the surface of the non-polar polymeric material with a low temperature microwave plasma generated in an LMP microwave plasma generator, in which a chemical compound has been introduced. The subsequently generated plasma is capable of creating receptor sites for acid dye on the surface of the non-polar polymeric material. The chemical compound useful in this novel method will be referred to hereinafter as the "plasma monomer".
Of great importance is the finding that the LMP treatment of a polypropylene fiber or fabric, either woven or non-woven, fiber or cloth, is sufficiently penetrant to all regions of the fiber or cloth such that cross-over regions are equally affected by the treatment, but can retain, unaffected, the mechanical and thermal properties of the fiber and/or fabric.